Description
MIT krb5 through 1.22.2 contains a NULL pointer dereference vulnerability in the KDC's get_pac_princ_with_realm() that returns success while leaving the client principal NULL on malformed names. A malicious or compromised cross-realm trusted KDC can send an S4U2Proxy request with a PAC carrying a malformed client name to crash krb5kdc and deny authentication.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| MIT | krb5 | ≤ 1.22.2 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | krb5 | No fix yet | — |
| Debian 13 | krb5 | No fix yet | — |
| Debian 12 | krb5 | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | krb5 | No fix yet | — |
| Ubuntu 26.04 LTS | krb5 | No fix yet | — |
| Ubuntu 24.04 LTS | krb5 | No fix yet | — |
| Ubuntu 22.04 LTS | krb5 | No fix yet | — |
| Ubuntu 20.04 LTS | krb5 | No fix yet | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 18.04 LTS | krb5 | No fix yet | — |
| Ubuntu Pro 16.04 LTS | krb5 | No fix yet | — |
| Ubuntu Pro 14.04 LTS | krb5 | No fix yet | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | krb5 +8 | 1.21.3-11.el10_3.2 | RHSA-2026:99624 |
| RHEL 9 | krb5 +8 | 1.21.1-10.el9_9.2 | RHSA-2026:99715 |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10.2 EUS | krb5 +8 | 1.21.3-10.el10_2.2 | RHSA-2026:99625 |
| RHEL 9.8 EUS | krb5 +8 | 1.21.1-10.el9_8.3 | RHSA-2026:99716 |
| Red Hat Hardened Images 1 | krb5 +9 | 1.22.2-10.3.hum1 | RHSA-2026:97811, RHSA-2026:80481 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | libkadm5 +7 | 1.21.3-11.el10_3.2 | RLSA-2026:99624 |
| Rocky Linux 9 | libkadm5 +7 | 1.21.1-10.el9_9.2 | RLSA-2026:99715 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLE Micro 5.5 | krb5 | 1.20.1-150500.3.26.1 | SUSE-SU-2026:4906-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | krb5 | 1.22.3-r0 | — |
| Alpine v3.23 | krb5 | 1.22.3-r0 | — |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | krb5 | No fix yet | — |
Advisories 11
- RHSA-2026:99625 Red Hat Security Advisory: krb5 security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:99624 Red Hat Security Advisory: krb5 security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:97811 Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:99716 Red Hat Security Advisory: krb5 security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:99715 Red Hat Security Advisory: krb5 security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RLSA-2026:99715 Important: krb5 security, bug fix, and enhancement update Rocky Linux Security Advisories · Nov 13, 2026
- RLSA-2026:99624 Important: krb5 security, bug fix, and enhancement update Rocky Linux Security Advisories · Nov 13, 2026
- WID-SEC-2026-3836 MIT Kerberos: Mehrere Schwachstellen ermöglichen Denial of Service BSI CERT-Bund (WID) · Nov 12, 2026
- WID-SEC-2026-4435 MIT Kerberos: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- SUSE-SU-2026:4906-1 Security update for krb5 SUSE / openSUSE Security Updates · Oct 26, 2026
- RHSA-2026:80481 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 14, 2026
References
- Pull Request #1510 issue-tracking patch
- Patch Commit patch
- https://github.com/krb5/krb5/commit/a88a18cafa1040a0c4f9c8d08288fc98831ec86d patch
- https://github.com/krb5/krb5/blob/krb5-1.22.2-final/src/kdc/kdc_util.c#L639-L676 technical-description
- https://github.com/krb5/krb5 product
- VulnCheck Advisory: MIT krb5 through 1.22.2 KDC NULL Pointer Dereference via S4U2Proxy PAC third-party-advisory